Conventional wisdom holds that the more powerful a telephoto lens you mount on your camera, the more you may need a tripod for shake-free images. With patience and breath control many photographers have long been able take crisp handheld shots with lenses of focal lengths up to 400mm. That ability can now be extended to almost everyone through technology. The best modern DSLRS can produce crisp handheld images with short exposures at high ISO settings and, coupled with good image stabilization lenses, can effectively expand the focal length (or power, if you will) of lenses that can be used to advantage without a monopod or tripod.
For a general purpose telephoto lens, this 70-300mm zoom can't be beat. In my experience the optics have produced crisp images at any focal length and at most aperture settings, though images taken with apertures at the middle of its range (f/11, for example) appear just slightly sharper than ones taken with a wide open lens.
Canon has thoughtfully included two different image stabilization modes for the benefit of individuals who use the lens in different ways. Mode 1 is for general purpose image stabilization when the camera is held still to capture a stationary field of view. Mode 2 is used for panning shots in which the photographer is following an item or individual in motion. This mode locks out attempts to correct for blur in the direction of camera motion. And you can of course lock out IS altogether if you are so inclined. Autofocus can also be locked out in case you are shooting nearby objects from a tripod and want to pick the exact focal point of the image field yourself. The word "macro" is printed on the lens, but that strikes me as a little aspirational. I would consider this lens a close-focusing zoom, as you can get fairly close-up images of smaller objects that are a little distance away. Minimum focusing distance is just under five feet, and at that distance the 300mm setting will let you fill the frame with an object about five inches wide. This could be a good lens to capture images of large winged insects and even hummingbirds, as those interesting subjects are notoriously intolerant of close approach by photographers. For true macro photography of flower details or smaller insects, you should mount a different lens.
Build quality is excellent, options for use are rich, optical performance is excellent and the lens, though not tiny or light, is compact and manageable. Canon makes other, more expensive lenses with similar design features that might better satisfy the most critical photographers, but in light of the relatively low cost of this lens and its great flexibility, this has to be one of the best general purpose lenses that Canon manufactures.